Not possible for bigger flash because the chip limitation. But you can use SD card or USB and install your program on it.

The methods:

  1. First mount USB/MicroSD card, e.g. as /mnt/sda1
  2. in /etc/opkg.config, add one line with contents:
    dest usb /mnt/sda1
  3. When install packages, add path, e.g.

opkg install xxxx -d usb 

More help can be found: OPKG Package Manager [Old OpenWrt Wiki]